Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
  • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
  • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
  • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
  • H01L31/109—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN heterojunction type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
  • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
  • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
  • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
  • H01L31/103—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN homojunction type
  • H01L31/1035—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN homojunction type the devices comprising active layers formed only by AIIIBV compounds
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
  • H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
  • H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
  • H01L29/201—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds including two or more compounds, e.g. alloys
  • H01L29/205—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds including two or more compounds, e.g. alloys in different semiconductor regions, e.g. heterojunctions
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
  • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
  • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
  • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
  • H01L31/105—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PIN type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
  • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
  • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
  • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
  • H01L31/108—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the Schottky type
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/548—Amorphous silicon PV cells

Definitions

• This invention relates to (InGa)As-lnP heterojunction devices utilizing a lnP: ⁇ collector to extract electrons from a (lnGa)As:p layer and more particularly to heterojunction devices having a smooth and monotonic potential energy gradient at the heterojunction for establishing drift of the conduction electrons from the (lnGa)As:p layer to the lnP: ⁇ layer.
• these and other objectives are achieved by interposing a semiconductor alloy grading layer and an n-type InP built-in field layer between the (lnGa)As:p layer and the lnP: ⁇ layer of the heterojunction device.
• a semiconductor alloy grading layer is grown in which the composition of the alloy is controlled so that the electron affinity of the alloy gradually varies from that of the (lnGa)As:p layer to that if the lnP: ⁇ layer.
• Examples of semiconductor alloy systems appropriate for this layer include ln ⁇ G a ⁇ -yAs i -yP y and (AlsG a i -s)l -tlr>tAs where x and y or s and t, the alloy constituent fractions, are varied to yield the proper electron affinity variations.
• the two alloy fraction variables in these quaternary alloys provide for the required variation in electron affinity with an additional degree of freedom provided to meet other growth constraints.
• An example of such an additional constraint might be the requirement that a uniform lattice constant be maintained throughout the grading layer growth.
• an n- type InP layer is grown to provide the built-in field, and the undoped InP collector layer is grown.
• the dopant concentration in the p-type alloy grading layer and the n-type InP built-in field layer, the thicknesses of these layers, and the profile of the compositional variation with position in the alloy grading layer are all chosen such that the conduction band energy exhibits a gradual decrease from the (lnGa)As:p layer to the lnP: ⁇ layer under the influence of any externally applied voltages to be used in the final device operation.
• this will require that both the semiconductor alloy grading layer and the lnP:n built-in field layer are fully depleted with a gradual drop in the conduction band energy from the (lnGa)A:p to the lnP: ⁇ with no externally applied voltages.
• Additional layers may be grown on the lnP: ⁇ layer as dictated by the final device design.
• this invention could be implemented by starting with the lnP: ⁇ layer and reversing the order of deposition of the layers and the alloy constituent profile of the alloy grading layer.
• Conduction electrons introduced through photoabsorption throughout the bulk of the (InGa)As layer or introduced at a buried junction through the application of a forward bias, as in a heterojunction bipolar transistor, are directed to the heterojunction under the influence of a diffusion current and through the heterojunction under the influence of a drift current.
• the utility of the present invention is directed primarily to the efficient transfer of electrons at (lnGa)As/lnP heterojunctions
• the most general form of this invention is applicable to a wide variety of semiconductor heterojunctions.
• the present invention has application to any heterojunction wherein it is desired to efficiently transfer electrons from a small-bandgap, large electron affinity p-type semiconductor to a large-bandgap, small electron affinity undoped or n-type semiconductor.
• the implementation of this invention requires only that a gradually graded alloy or virtual alloy be grown at the heterojunction which provides electron affinity matches to the two semiconductor materials.
• heterojunction systems which are appropriate for this invention include the GaAs/(AIGa)As and
• GaAs/(lnGa)P systems GaAs/(lnGa)P systems.
• FIG. 1 is an schematic sectional view of the invention
• FIG. 2 is an energy level diagram of the conduction band in an implementation of this invention having a quadratic dependence of the alloy composition on position in the graded region under the condition of zero externally applied bias,
• FIG. 3 is a comparison of the quadratic and piecewise linear alloy composition grading profiles
• FIG. 4 is an equilibrium energy level diagram of the conduction band in an implementation of this invention having a piecewise linear dependence of the alloy composition on position in the graded region under the condition of zero externally applied bias
• FIG. 5 is a schematic sectional view of a p-i-n photodiode structure incorporating the invention
• FIG. 6 is an energy level diagram of the p-i-n diode of FIG. 4 under the condition of zero externally applied bias
• FIG. 7 is a schematic sectional view of a transferred electron photocathode structure incorporating the invention.
• FIG. 8 is an energy level diagram of the transferred photocathode of FIG. 6 under the condition of 2.1 volt externally applied bias.
• FIG. 1 there is shown the schematic sectional view of the present invention including the semiconductor alloy grading layer 16 and the lnP:n built-in field layer 18 interposed at the junction between the p-type (InGa)As layer 14 and the undoped InP layer 20.
• the grading layer in this structure is comprised of a semiconductor alloy whose composition can be adjusted to yield an electron affinity equal to that of the large band gap material such as InP for one composition and that of the small band gap material such as (InGa)As for another composition subject to any other constraints imposed by the growth process or device design.
• a lattice match to InP can be maintained approximately for a indium fraction of 0.532 independent of the relative compositions of aluminum and gallium.
• An additional method of implementing the semiconductor grading layer 16 is to utilize a superlattice having spatially varying layer thicknesses to produce a virtual alloy having the desired gradual change in electron affinity.
• a superlattice consisting of (lnGa)As:p wells and lnP:p barriers could be used with gradually varying layer thicknesses to implement the desired electron affinity variation.
• Near the (InGa)As p-type layer such a superlattice would consist of relatively thick wells and thin barriers to yield a virtual alloy which is arbitrarily close in electron affinity match to the (InGa)As layer.
• the superlattice Near the end of the graded region, the superlattice would consist of relatively thin wells and thick barriers to yield a close electron affinity match to InP.
• the well and barrier thicknesses would be varied to yield a virtual alloy having the desired electron affinity profile appropriate for this invention.
• the ability to spatially distribute the conduction band discontinuity constitutes one requirement of the present invention. Another requirement is the ability to provide an electrostatic potential energy which at all positions in the grading layer overcomes the chemical potential energy either through building-in such an electrostatic potential or through the application of external biases. In this way, there is a gradual decrease in the electrochemical potential for conduction electrons passing from the
• (lnGa)As:p to the lnP: ⁇ an adequate electrostatic potential is provided by the equilibrium depletion of the lnP:n built-in field layer so that no external bias is required to eliminate conduction band barriers to the drift of electrons from the (InGa)As to the InP.
• This embodiment necessitates the thickness of the grading layer being less than or equal to the depletion depth into the p-type layer caused by the InP.n built-in field layer and additional layers of the total device structure, and that the lnP:n built-in field layer is fully depleted under the condition of no applied bias.
• the depletion depths will be approximately 55 ⁇ A into the grading layer and 22 ⁇ A into the built-in field layer.
• a grading layer which is less than or equal to 55 ⁇ A thick and a built-in field layer which is 22 ⁇ A thick are appropriate.
• Such a junction provides a built-in potential of 0.87V, of which 0.40V drops across the graded region. This net electrostatic potential energy drop of 0.40eV is more than sufficient to overcome the 0.22eV net chemical potential energy increase in the graded region.
• ⁇ E C h ⁇ (1 + — r x r
• ⁇ is the net chemical potential energy difference across the graded region (equivalently, the conduction energy band discontinuity or electron affinity difference between (InGa)As and InP) and is equal 0.22eV for the lattice-matched alloy.
• FIG. 2 is a conduction band energy diagram for the structure presented in FIG. 1 with the dopant concentrations and quadratic alloy composition profile stated above. 1 1
• the (InGa)As layer is in the region x ⁇ -55 ⁇ A
• the alloy grading layer is in the region -55 ⁇ A ⁇ x ⁇ 0
• the depleted InPrn layer is in the region 0 ⁇ x ⁇ 22 ⁇ A
• the undoped lnP: ⁇ layer is in the region x>22 ⁇ A.
• the former 0.18eV potential energy drop is merely the net electrochemical potential energy drop ⁇ - ⁇ stated above.
• quadratic compositional grades are clearly sufficient for the graded alloy region of the present invention, they are not necessary and are non-trivial to implement during the structure growth. Numerous other suitable grading profiles are readily conceived which will create the desired effect of a smooth monotonic drop in the electrochemical potential for conduction electrons.
• One example of such an alternate composition profile is the piecewise linear profile defined as
• the graded layer, layer 16 of FIG. 1 would consist of a partial grade of p-type alloy and the built-in field layer, layer 18 of FIG. 1 , would consist of the remainder of the alloy grade having n-type doping.
• This approach has the advantage of keeping all of the electrostatic potential drop in the region where the chemical potential increase is occurring rather than having a portion of the electrostatic potential drop occur in a region of constant chemical potential.
• the application of the present invention to a p-i-n photodiode structure and a transferred-electron photocathode structure are shown in schematic cross-section in FIG. 5 and FIG. 7 respectively. In FIG.
• FIG. 5 is shown the back-surface contact 10, lnP:p substrate 12, (InGa)As absorber layer 14, semiconductor alloy grading layer 16, built-in field layer 18, lnP: ⁇ drift region 20, lnP:n+ contact layer 22, and top surface ohmic contact metal 24.
• Light which is incident on the top layer of this structure will generate photoelectrons in the (InGa)As absorber layer 14 which must pass through the lnP: ⁇ drift layer to contribute to the photocurrent of the device.
• the present invention provides efficient transfer of the photoelectrons from the absorber layer to the drift layer through the elimination of potential barriers and trapping discontinuities.
• the band diagram for one design of such a device is presented in FIG.
• the transferred electron photocathode structure of FIG. 7 consists of a glass window 30, lnP:p- substrate 32, substrate ohmic contact 34, absorber layer 14, semiconductor grading layer 16, built- in field layer 18, lnP: ⁇ drift region 20, high-field lnP:p layer 44,
• the elimination of potential barriers to photoelectrons drifting from the absorber layer to the drift layer is clear from the conduction band of this diagram..
• the objects of this invention have been achieved by providing a gradient in potential energy for conduction electrons travelling from an (InGa)As layer to an lnP: ⁇ layer for the purpose of increasing the efficiency of the electron collection.
• the current invention allows for the use of extrinsic low bandgap (InGa)As absorber layers and depleted large- bandgap lnP: ⁇ layer to reduce the collection of thermally generated current from depleted low-bandgap material, reduce the capacitance of the aggregate heterojunction, and improve the time response junction.
• this invention can be used to efficiently transfer electrons from a small-bandgap large electron affinity semiconductor to a large-bandgap small electron affinity semiconductor.

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• 1994
  • 1994-11-01 US US08/332,880 patent/US5576559A/en not_active Expired - Lifetime
• 1995
  • 1995-10-25 EP EP95938897A patent/EP0789935B1/de not_active Expired - Lifetime
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